The present invention relates to a liquid distributor that is designed to be situated between packed beds in order to ensure mixing and redistribution of liquid. More particularly, the present invention relates to such a liquid distributor having a predistributor trough for distributing the liquid to rows of apertures. More particularly, the present invention relates to such a liquid distributor in which the predistributor trough has bottom and side openings from which liquid is distributed onto the liquid distributor and rows of apertures.
Distillation is effected by contacting vapor and liquid phases of the mixture to be separated in a distillation column. The vehicle for effectuating contact and therefore, the mass transfer between liquid and vapor phases, can be by a variety of known random and structured packings that are arranged in beds within the distillation column. The beds function to allow formation of a liquid film that descends through the packing. A consequence of the formation of the film is that the liquid tends to spread out in the packing and flow towards the walls of the column. Additionally, any maldistributions of liquid that are retained as liquid is fed from bed to bed lead to changing liquid concentrations as one travels across the beds in a transverse direction of the column.
Liquid distributors are provided between packing beds in order to ensure mixing and redistribution of the liquid. Liquid distributors can be in the form of liquid distributor trays or liquid distributor troughs that are employed with liquid collectors to collect the descending liquid phase of the mixture. Known liquid distributor trays consist of a plate having rows of apertures for the liquid to descend from the plate to the next underlying bed of packing. Additionally, rows of vapor risers are provided between the rows of apertures to allow a vapor phase of the mixture to ascend through the distributor tray. Liquid distributor troughs include a trough network having parallel, elongated troughs provided with rows of apertures. The distributor troughs are spaced to allow for the ascending vapor phase of the mixture to pass between troughs.
In order to introduce liquid onto the liquid distributor in some orderly fashion and such that liquid is distributed to all the rows of apertures, a predistributor trough can be provided between the vapor risers of a distributor tray or overlying the trough network of a distributor trough. Predistributor troughs are provided with bottom openings to distribute liquid onto the distributor tray or trough network. In order to accommodate high flow rates, it is common to notch the lateral top edges of the predistributor trough so that liquid may overflow the predistributor trough directly onto the distributor tray or trough network in an orderly fashion. It is also known in the art to size the bottom openings so that a greater open area exists at central locations thereof. The reason for this is that for a circular distributor tray design or a trough network designed to fit within a cylindrical distillation column, there are more apertures at such central locations and hence, a greater flow requirement to accommodate the increased number of apertures.
The inventors herein have identified problems in prior art predistributor trough designs that tend to promote mal-distributions of liquid. One problem centers on the bottom openings. The flow of liquid from the bottom openings induces a velocity distribution, within the liquid flowing across the distributor tray or troughs of the distributor trough, in which liquid velocity is greatest near the surface of the tray or trough network. This velocity distribution induces a greater flow to outlying apertures. Another problem is that during overflow operation, the flow of liquid from the regularly spaced notches induces an even flow rate of liquid from the predistributor trough. Such an even flow rate can cause liquid to circulate around the distributor tray rather than being equally distributed to all of the apertures.
As will be discussed, the present invention provides a liquid distributor in which the redistributor trough is designed to promote uniform velocity profiles of liquid and therefore uniform distribution of the liquid.